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Diffstat (limited to 'kernel/gdt.h')
| -rw-r--r-- | kernel/gdt.h | 36 |
1 files changed, 36 insertions, 0 deletions
diff --git a/kernel/gdt.h b/kernel/gdt.h new file mode 100644 index 0000000..03f575e --- /dev/null +++ b/kernel/gdt.h @@ -0,0 +1,36 @@ +#ifndef _GDT_H_ +#define _GDT_H_ + +// Structure of a GDT descriptor. There are 2 types of descriptors: segments and TSS. +// Section 3.4.5 of Intel 64 & IA32 architectures software developer's manual describes +// segment descriptors while section 6.2.2 describes TSS descriptors. +typedef struct gdt_entry_st { + uint16_t lim15_0; + uint16_t base15_0; + uint8_t base23_16; + + uint8_t type : 4; + uint8_t s : 1; + uint8_t dpl : 2; + uint8_t present : 1; + + uint8_t lim19_16 : 4; + uint8_t avl : 1; + uint8_t l : 1; + uint8_t db : 1; + uint8_t granularity : 1; + + uint8_t base31_24; +} __attribute__((packed)) gdt_entry_t; + +// Structure describing a pointer to the GDT descriptor table. +// This format is required by the lgdt instruction. +typedef struct gdt_ptr_st { + uint16_t limit; // Limit of the table (ie. its size) + uint32_t base; // Address of the first entry +} __attribute__((packed)) gdt_ptr_t; + +extern void gdt_init(); +extern void gdt_flush(gdt_ptr_t *gdt_ptr); + +#endif |